<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>伪类选择器</title>

    <style>
        div{
            width: 500px;
            height: 500px;
            background: green;
        }
        div:hover{
            width: 250px;
            height: 250px;
            background: red;

            }

    </style>
</head>
<body>
<div></div>


</body>
</html>